So what does 6 cents mean for a school trying to make lunch healthier for its students? It can be the difference between buying wheat bread or white bread. Or between fresh vegetables and canned. But it can’t be both, not at the same meal. While making only one of those switches would benefit students, making both would be better.

That’s one of the challenges facing the Healthy, Hunger-Free Kids Act, the bill passed this month by Congress that aims to overhaul school food programs with the goal of reducing childhood obesity and making sure children in need receive proper nutrition.

The bill, which President Barack Obama is expected to sign today, would create healthier standards for school meals. It would increase funding by 6 cents per meal and do more to let schools know when a student qualifies for a free or reduced-price meal.

On the whole, experts and school districts said the bill is a big step toward raising healthier kids. But, they said, hurdles will remain. Among them:

— The cost of fresh fruit and vegetables. It’s higher. It also costs more to prepare food from scratch than to reheat frozen foods, which are often loaded with sodium and have too much fat. The 6-cent increase can cover some of that difference, but not all of it.

— The U.S. Department of Agriculture’s commodity program. Many schools rely on this money to fill out their cafeteria budget, but the program’s rules require districts to spend money on things such as chicken nuggets.

— The final lunch rules. The bill sets guidelines based on recommendations by the Institute of Medicine, but the USDA has said it wants input from all stakeholders, including schools and food companies, the latter of which make big money supplying cafeterias across the country.